I asked if there were plans to introduce the .40-caliber models in Gen 5, and the Glock rep told me probably not yet - because they also got rid of the locking block pin (another throwback to the Gen 2 days), which was primarily added for the .40-caliber and .357 SIG Glocks. So at the very least, they'll have to keep producing Gen 4 Glocks in the larger calibers until they solve the engineering challenges associated with removing the locking block pin on the 9mm Gen 5s.

I mean, I can see why they wouldn't make .40's, but c'mon now get them 10mms and .45s out on the market, Gaston

While Glock doesn’t release sales data, I imagine that their .40 S&W pistols are still outselling the 10mm and .45 ACP models (though of course, sales have probably started dropping since the market is moving away from .40). So economically, it would make more sense to produce the .40s first.